Lamp



April 9, 1.940. 1 5, mm. 2,196,567

F1166. July 27, 1937 2 Sheets-Sheet 1 Patented Apr-.9, 1940 UNITEDSTATES;

PATENT OFFICE LAMP George Sperti, Cincinnati, Ohio, assignor to SpertiLamp Corporation, New York, N. Y., a a corporation of DelawareApplication July 27, 1937, Serial No. 156,025

24' Claims...

This invention relates to electric light sources of the type embodyingan arc, for example, an arc in mercury vapor which provides a source ofultra-violet radiation. This application is a continuation in part of myprior application,

- 0 in low regions, particularly where the atmos- 30 2,046,096, thereare disclosed lamps adapted for general use under the same conditions asthe ordinary incandescent lamp and' reprodwcing substantially the solarspectrum. These lamps embody an'incandescent elementas a source of 35visible radiation and an are as a source of ultraviolet radiation, theradiation from these two sources being combined and filtered so that it.about 2950 Angstrom units. The light from 40 these sources is or whitecolor and closely readapted for use in such alamp but also suitable foruse per se when the radiation of the incandescent filament is notneeded. In accordance with the present practice of making incandescent55 lamp the incandescent filament is of tungsten (01.1'16-1) andispreferably operated at high temperature plications, and to a novel areunit particularly in a high pressure atmosphere to increase theefllciency of the lamp. In a low pressure ata gaseous discharge,however; such a filament tends to evaporate quickly, causing prematuremosphere such as is desirable for the starting of destruction of thefilament and blackening of the lamp bulb. By enclosing the filament andthe arc in .separate chambers within the lamp, the filament chambermayhave a relatively high pressure gas filling such as to preventevaporation of the filament while the arc chamber may be adjusted to theoptimum pressure for starting the gaseous discharge. j

Another reason for operating the incandescent filament at hightemperature is that a filament of this kind emits more shortwave energyas its temperature increases. A tungsten filament at the temperaturesfound in the ordinary incandescent lamp emits in a substantiallycontinuous spectrum down to about 3000- Angstrom units, and although theamount of energy at the extreme short end of the spectrum is small, itis desirable to'preserve these short wave radiations in the lightemitted by the lamp because of their therapeutic value. In the ordinaryincandescent lamp, these short wave radiations are largely absorbed bythe glass bulb, but by the use of an ultra-violet transmitting glassthey can be emitted with beneficial results. Preferably, however, theshort wave energy of the tungsten filament should be-supplemented byshort waves from some ultra-violet source such as an are in a suitableatmosphere such as mercury.

Since such an arc emits radiations of wave.

'lengths below 2950 Angstrom units and hence objectionable, itbecomesdesirable to filter the does not contain wave lengths shorter than arcradiation in order to prevent the emission of harmful short waves.transmit freely to the desired short wave length "limit and would beentirely opaque beyond this limit, but the available filter materials donot cut oil sharply so that in order to prevent the transmission ofundesirable wave lengths it is necessary to sacrifice a part of thedesirable wave lengths. For example, when a mercury arc is used, thefilter must absorb substantially all radiations shorter than about 2950Angstrom units and filter materialsjwhich positively absorb all energybelow this point will also absorb a material portion ofthe desirableenergy above this point. This'means that the energy both of the are andof the incandescent fila- An ideal filter would ment is partiallyabsorbed in the region immediately above 2950 Angstrom units, or inother the radiation from the are without afiecting the radiation fromthe filament. In this way all of the beneficial radiation from thefilament is preserved and emitted without filtering, while the desiredportion of the arc radiation is transmitted. through the filter andsuperposed on the filament radiation and the undesirable portion of thearc radiation is absorbed by the filter.

Another object is to provide a lamp of the type described embodying anare enclosed in an inner chamber within the lamp bulb and surroundedbya. filtering medium together with a. filament in the outer chambersurrounding the are.

.A further object is to provide an improved lamp of novel constructionwhich operates efficiently and may be constructed cheaply andeconomically and which is well-adapted for quantity production methodsof manufacture.

In connection with alamp of the type characterized above, as well aswhen the arc only is desired without an incandescent filament, it isdesirable to'provide an arc unit such that the are always strikes atorbelow approximately volts. Glow discharge lamps wherein the discharge isestablished and maintained by electronic emission from a heated cathodewill operate at less than 110 volts. However, such glow dischargedevices are not suited for the purposes ofv the present inventionbecause in a small enclosure the walls of the container rapidly' blackenand also because the energy is concentrated in the less desirable shortwave radiation.

Accordingly, another object of the invention is to provide a novel areunit wherein the gaseous discharge is not dependent on electronicemission from a cathode but takes place by ionic conduction in a gaseousatmosphere.

Another object is to provide an arc unit'of the above type wherein novelmeans are provided to insure reliable starting of the arc.

A further object is to provide a novel are unit wherein the operatingpressure is high enough that the discharge has the characteristics of aconstricted are as distinguished from a glow discharge.

A further object is to provide a novel arc unit wherein no blackeningtakes place.

A still further object is to provide a lamp embodying a filament and arewherein the arc is embodied in a self-contained unit which can bemanufactured and tested separately before being placed in the lamp, orused separately in combination with any suitable current limiting means,for example, a separate incandescent filament lamp.

Another object is to provide a lamp having an arc and an incandescentfilament enclosed in separate chambers and so constructed that the heatfrom the incandescent filament tends to keep the arc chamber at theproper temperature for efiicient arc operation.

Still another object is to keep the arc chamher at a relatively.hightemperature by subjecting it to external heatfrom the incandescentfilament and insulating the arc chamber to prevent conduction of heattherefrom, whereby uniform heating of the entire arc chamber is obtainedto produce the desired vapor pressure.

Several embodiments of the invention have been illustrateddiagrammatically in the accompanying drawings, wherein Figs. 1 and 2 arerespectively a perspective view and a sectional view of a lamp embodyingthe invention; Figs. 3 and 4 are respectively similar views of anotherlamp embodying the invention; Fig. 5 is a detail view of a modificationof the lamp shown in Figs. 3 and 4; and Fig. 6 is a diagrammatic view ofanother embodiment of the invention; but it is to be expresslyunderstood that said drawings are for purposes of illustration only andare not to be construed as a definition of the limits of the invention;reference being had to the appended claims for this purpose.

Referring first to Figs. 1 and 2, the lamp bulb i may be of any suitablesize or shape and may be mounted in any suitable base 2 which as shownis of the conventional screw type adapted to be screwed into theordinary lamp socket 3. The bulb I may be of any suitable materialprovided only that it transmits the desired ultraviolet radiation.Various ultra-violet transmit-- ting glasses are known. Quartz glasstransmits.

freely down to below 2000 Angstrom units, and other glasses are knownwhich transmit freely to points well below 2950 Angstrom units. Aspecial glass known as corex transmits freely down to about 2800 or 2900Angstrom units and absorbs strongly in the shorter wave lengths. Where aglass such as corex is used for the bulb, it constitutes an additionalfilter which absorbs the undesirable. short wave lengths, but it is notessential that the material of the bulb have filtering characteristics.The bulb may also be frosted or not as desired.

Fused in the neck of the bulb l is the usual standard or stem 4 whichserves as a support for the various elements within the lamp and as ameans for introducing the conductors into the' lamp. In the form shown,in accordance with the usual practice, the stem is fused integrally at 5with the neck of the bulb l and conductors, 6 and I, connectedrespectively with the screw shell 2 and with the contact 8, extendthrough the standard and are fused therein. Within the bulb I is afilament 9 of any suitable type, size and shape. For example, a tungstenfilament having the form of a ring is supported at its opposite ends bythe conductor 6 and by a wire H) the end of which is fused in the stem4. Filament 9 may also be supported by a plurality of wires l lcentrally supported at II on a member to be described hereinafter which,as respects the supporting of the filament, is the counterpart of theglass rod that is secured to the stem'4 in the ordinary incandescentlamp. Preferably the bulb l is evacuated and filled with an inertgassuch as nitrogen, argon, etc., at a relatively high pressuresufficient to prevent substantial evaporation of the filament, whichpressure may for example be near atmospheric. This permits operation ofthe filament at high temperature without excesdescent filament 8 andlikewise topermit the If 2,190,507 maintenance independently or apressure suitable ent of one another the filament chamber pressure maybe low if desired and the arc chamber pres sure may have any desiredvalue; The are enclosing bulb or chamber may be of any suitable type,size and shape and may be mounted within the lamp in any suitablemanner. In the form shown, the glass rod that is employed as a filamentsupport in the usual incandescent lamp is replaced by an assemblycomprising a bulb l3 and a supporting stem l4 secured to the standard I,the upper end of the bulb i3 constituting the filament support i2referred to above.

The bulb i3 may be of any suitable material which transmits the desiredultra-violet radiations, such as any known ultra-violet transmittingglass, in which case the bulb is provided with an external filter l5which absorbs substantially all wave lengths shorter than 2950 to 3000Angstrom units. As filter materials, a thin sheet of mica gives goodresults,or the bulb it may be coated with various suitable transparentvarnishes, preferably of cellulosic base, impregnated or not with asuitable salt which provides the desired absorption. The mica (orvarnish, etc.) may be on the inside of the bulb i3 instead of on theoutside if desired, as described hereafter in connection with the lampshown in Fig; 4. If the bulb l3 4 is formed of a material havingfiltering characteristics, as for example corex, it may not be necessaryto add the filtering shield i5 particularly if the thickness of the bulbis increased. Where thin corex is employed, however, it is preferable touse the filter l5 because the thin corex does not positively absorb allof the objectionable short wave energy. The supporting stem ll may be ofthe same material as the bulb l3 and may be fused to the bulb and to thestandard 4, but it will be understood that metallic or other supportsmay be employed for the bulb.

As indicated above, it is desirable to provide an arc unit wherein thedischarge has the characteristics of a constricted arc as distinguishedfrom a glow discharge and wherein the discharge takes place by ionicconduction so that electronic emissi'oii from a heated cathode'is notnecessary. In such a lamp the electrodes may have any suitable form andmay suitably comprise coils or grids of wire such as tungsten or thelike which are proportionedto operate cold or at least at a suiflciently low temperature that there is no evaporation of the electrodematerial. To secure starting of the min such a device, however, it isnecessary to provide for activation of the electrodes and to this endthe electrodes are located in proximity to a quantity of thermionicallyactive oxide and provision is made for heating this oxide @to arelatively high temperature during an initial processing or activatingoperation. It has been found that after such activating operation, the.

arc will start between the electrodes as soon as the current is turnedonv without any heating of 1 trodes, and the filaments 22 and 23remaining '10.

the oxide, i

In the construction shown in Figs. 1 and 2, provision is made forheating the thermionically active oxide by a heater circuit in serieswith the incandescent filament 9 to accomplish the desired activation ofthe electrodes during the filament circuit and an' arc isestablished atrelatively high voltage until activation takes place. i

'is increased the are concentrates between sleeves l6 and i1 areheatedby internal filaments 22 and 23, filament-23 being connected at one endby means of a conductor 2| with the end of the filament 9 and at theother end by a conductor 25 with one end of the filament 22 and theopposite end of filament 22 being connected by a conduc tor 26 with theconductor 1. It will accordingly be seen that filaments 9, 23 and 22 arein series and that when current passes through this circuit, filaments22 and 23 become hot and heat thetubes l6 and IT. The sleeveiG isconnected by a cond tor 21 with the conductor 26, while the sleeve i isconnected by a conductor 28 with the conductor 24, these connectionsbeing arranged so that the potential drop through the filaments 22 and23 is impressed across the sleeves and the electrodeshereinafter'described. To increase the potential drop a resistance 29may be inserted in the lead 25, whereby any desired drop may be providedwhile at the same time the heating filaments 22 and 23 may be properlyproportioned according to thescharacteristics of the sleeves to give theproper heating effect.

The are chamber i3 is preferably evacuated to a point suitable foreflicient arc operation and contains a quantity of'ionizable materialwhich radiates in the ultra-violet region of the spectrum. A convenientmaterial for this purpose is is notoperating. Should the quantity ofmercury vapor exceed somewhat the amount which can be maintained in thearc chamber in the form of vapor at ordinary temperatures, itwill bead-' sorbed by the elements in the bulb and will condense on the wallsof the bulb and then will be vaporized on heating.

In the-form shown in Figs. land 2, the electrodes have the form of fiatcoils or grids 3i and '32 which are supported from the tubes i6 and I1and are electrically connected therewith and with the filament circuitby suitable wires 33 and '34. y

In the initial activating operation, the oxide coatings on the tubes i8and Il' are heated by. the

Thereafter the arc bulb isfurther evacuated and the mercury and neon orargon introduced,

whereupon the bulbis sealed. After this initial activating operation,the arc strikes quickly between the electrodes 3i and 32 as soon aspotential is applied and without allowing time for any, heating of thetubes Iiiand ii, the current passing through the gaseous path betweenthe eleccool. The arc starts-first in the neon or other gas, but as thevapor pressure of the mercury the electrodes as a mercury discharge.

The normal operation of a completed lamp may be summarized as follows,When the lamp is screwed into the socket 3 and current is turned on,potential is impressed across the leads 6 and I causing a potential tobe applied across the electrodes 3| and 32, the amount of which dependson the relative proportions of the filament 8 on the one hand and thecircuit 22, 29, 23 on the other hand. Preferably, these elements "areproportioned so that the potential across the electrodes is about 60volts or greater. The neon arc strikes immediately without anypreliminary heating of the sleeves l6 and I1. As the filament 9 isheated to incandescence, it imparts heat to the arc chamber I3 which,together with'the heat generated in the arc chamber itself by thedischarge current, causes the mercury vapor pres-.

sure to increase so that the arc is converted into a mercury discharge.

Figs. 3 and 4 illustrate a somewhat different construction for a lampembodying the invention. This lamp embodies a suitable base 2 and outerbulb I in which is enclosed an incandescent filament 35 of tungsten orthe like, said-filament ,being supported by wires 36 mounted on an innerbulb 31 and also by supporting wires 38 and 39. It will be understoodthat these elements preferably are the same as'those described above inconnection with Figs. 1 and 2. The are chamber or bulb 31 is in thisinstance supported by means of a band 40 of suitable metal whichsurrounds the base of the bulb and has .welded thereto supporting wires4| and 42 which are fused in the standard or stem 43 of the lamp.

Within the'arc bulb 31 is a pair of electrodes together with a quantityof mercury or other suitable material indicated graphically at 44whereby an arc is formed between'the electrodes. Adjacent the electrodesare sleeves or tubes 45 of suitable insulating material such as quartzglass, said tubes being surrounded by sleeves 46 of nickel or othersuitable material and said sleeves being preferably coated with an oxideor mixture of oxides such as strontium, thorium and barium as describedabove. Each tube 45 and its sleeve 46 are supported by means-of a pairof metal bands" suitably connected as by welding to a supportingwire 48that is fused in the usual standard or stem 49 of the inner bulb.- Theelectrodes themselves comprise grids 50 which in this case take the formof coils of wire such as tungsten surrounding the oxide sleeves andsecured to the supports 48 in any suitable manner as by welding. One endof the incandescent filament 35 is connected by a wire with the outerend of one of the supports 48, and the other support 48 is connected bya wire 52 with the lamp base 2. In this way potential is applied to theelectrodes to start an arc in the bulb 31, the potential drop betweenthe electrodes being established by a circuit within the bulb 31 whichis in parallel with the arc path and which comprises filaments forheating the oxide sleeves during the activation period. As shown, a wire53 connected to one of the supports 48 leads to a filament 54 positionedwithin one of the tubes 45. A conductor including a resistance 55connects the other end of filament 54 with a similar filament 56positioned within the other quartz tube 45, and the other end offilament 581s connected by a wire 51 with the support 48.

The resistance 55 is the counterpart of the resistance 29 shown in Figs.1 and 2, except that it is within the inner bulb 31 for' the purpose ofreducing the number of leads into the inner bulb and making it anentirely enclosed unit. However, if the arc strikes to the resistanceitself it will probably be burnt out very quickly. Hence the exposedresistance 55 is protected as by coating it with a cement such as thatknown as alundum which is insulating. and does not evaporate. Anothermeans of protecting the resistance 55 is shown in Fig. 5, wherein thequartz glass tubes 45 are connected by a tube 58 of any suitablematerial, the tubes 45 and 59 being preferably formed by tubing bentinto the form of a U.

The bulb 31 is preferably provided with afllter 58 which in thisinstance is within the bulb 31 .instead of outside it as described abovein connection with Figs. 1 and 2. The filter 58 therefore not only.assists in absorbing the short waves so that they are not emitted by thelamp but also protects the material of the bulb 31 from injurious shortwaves. It is well known that many ultra-violet transmitting glasses whenexposed for long periods to ultra-violet radiation undergo changes knownas solarization where by the transmission characteristics of the glassare altered. By placing the filter inside the bulb, solarization can besubstantially prevented.

Fig. 6 shows another embodiment of the invention wherein the arc elementis not contained within an outer bulb as in the embodiments previouslydescribed. As .shown in Fig. 6- the arc unit comprises an elongated bulb60 having an electrode at each of its ends. In the form shown .theelectrodes comprise wire coils 6| similar to the electrodes of Figs. 3and 4, said wire coils 6| being mounted by welding or otherwise onsupports 62 that are fused in the ends of the bulb 60 and constituteleads for applying potential to the electrodes. Within each electrode isan oxide coated sleeve or tube 63 containing a heater filament similarto those previously de- -'scribed. These sleevesi or tubes 63 are alsocarried by the supporting} wires 62 one end of each filament beingconnected to the support 82 and the other end of each filament to a lead64 passing through the end of the bulb. The filaments are connected inseries with one another by an external connecting wire 65 which maycontain a resistance 66 to adjust the potential applied across theelectrodes. This are unit is operated in series with a suitable externalcurrent limiting device such as an incandescent lamp 61. The operationofthe arc is the same as described above in connection with precedingembodiments, except that in this case the operating temperature of thearc is maintained only by the energy dissipated within the arc bulb.

The starting voltage for the arc is the sum of the voltage drops in theheating filaments and resistances therebetween and in a device designedto operate on house lighting circuits should be about 60 volts orgreater. It will beunderstood that the distribution of energy betweenthe incandescent filament and the arc may vary widely. For a '75 wattlamp, for example, the energy dissipated in the arc may be in theneighborhood of to 20 watts and the remainder may be dissipated in thefilament. v In an arc unitsuch as shown in Fig. 6, however, it may bedesired to dissipate much greater energy, for example, several hundredwatts. During operation of the lamp the arc chamber is maintained at atemperature high enough for eflicient arc operation since it issurrounded by the main filament and enclosed within the outer bulbwhereby there is substantial insulation against conduction away of heat.The heat provided in this way causes the are chamber to heat uniiormlythroughout so that the desired vapor 'pressurecan be maintained with avery small amount oi mercury and whereby the usual large pool ofunvaporized mercury is eliminated The radiation from the main tungstenfilament maybe emitted by the lamp without filtering and hence withoutabsorption of any of the available ultra-violet energytherefrom. Thispreserves in the emitted radiation the small amount of energy at theultra-violet end of the spectrum of the incandescent tungsten. Theradiation from the arc chamber, supposing mercury to be used, isfiltered through the walls of the arc'chamber and/or through the filtershield IE or 58 which effectively absorb all of the energyofobjectionable. short wave lengths. The are energy of longer wavelengths, however, both in the invisible ultra-violet portion of thespectrum and in the blue end of the visible spectrum, passes freelythrough the walls of the arc chamber and the filter I! or then throughthe outer bulb l.' x

The resultant spectrum of the lamp is the substantially continuousspectrum of incandescent tungsten having superimposed thereonthe arcenergy in the short wave length ultra-violet region and in the blue partof the visible spectrum so that the light from the lampapproachesnatural sunlight very closely in quality. The entire lamp isof simple construction and economical in manufacture. The ultra-violetelement can be manufactured separately from the incandescent element andtested separately before being incorporated in the lamp. The manufactureof the complete lamp is thereafter similar to the 58 and are activatedso that the arc strikes between them without allowing time for theheater filaments to heat the sleeves. This prevents disintegration anddestruction of the sleeves and provides long life. In view of thisoperation of the arc unit, it will be seen that the heater filaments arenot necessary except as a means or activating the sleeves or theelectrodes during the manufacture oi the lamp. This also makes forlonger life in that the lamp will continue to operate in the same mannerif the'heater filament circuit should be burnt out or destroyed duringactiva tion or thereafter. Since the oxide sleeves carry no arc current,it will also be seen that theyneed not be connected to the circuit.

While only three embodiments of the invention have been described andillustrated in the drawings it will be understood that the invention iscapable of a variety of physical expressions. The shape and size or thelamp and of the inner arc chamber and the materials used may be variedas desired. The shape and size of the incandescent filament, and thesize, type and form of the arc electrodes can also be varied as desired.The ionlzable material. within the arc chamber may be other thanmercury, and the type and characteristics of the filters l6 and 58 willdepend upon' the characteristics of the arc, and also on the efiect tobe produced. For instance, slight changes in the shortest transmittedwave length will cause varying degrees of tanning and erythema, and suchefl'ects can be controlled by the characteristics of the filter. Themostdesirable short wave length limit for general purposes is probablybetween 2950 and 3000 Angmethods now used for constructing the ordinarystrom units, but for some purposes it may be deincandescent lamp. Owingto the relatively high sired to emit waves as short as 2800 or 2850Anggas pressure within the filament chamber, the stromfunits. These andother changes, many of filament can be operated at high temperatureswhich will now occur to those skilled in the art,

without danger of blackening of the lamp chamher or of prematuredestruction oi the filament, thus providing greater operating emciencyand greater .emission of the short wave length energy.

At the same time conditions within the arc chamber are such as toprovide for efliclent operation and there isno possibility of contact ofthe ionlzable material with thernain filament nor of arcing to or fromthe main filament. Due to these features, the lamp may be operateddisealed inner bulb, an incandescent filament in said outer'bulb, a pairof arc electrodes in said inner bulb, said inner bulb also containing apair of, thermionically active elements and heatin rectly from 110 voltsand hence can be used in filaments therefor, a resistance outside saidinthe ordinary damp socket without damage. ner bulb and connectedbetween said heatin Since the light in the lamp is of white color, andfilaments in series, the circuit comprising said since the outer bulbmay if desired be frosted, the heating filaments and resistance beingconnected illuminating eflect is the same as that produced in serieswith said incandescent filament between .by the modern incandescent lampexcept that the light shades more toward white than the light from atungsten filament due to the additional energy in the blue portion ofthe visible spectrum. If desired, the outer bulb may be left transparentwhile the inner bulb is frosted preferably on its outside. Thisprocedure hides from view the elements within'the inner bulb anddifiuses the illumination from the arc, giving the lamp a the terminalsof the lamp, said electrodes being connected to said heating filamentswhereby the potential drop through said heating filaments and resistanceis impressed across said electrodes.

2. A lamp comprising a closed outer bulb containing an incandescentfilament, a closed-inner bulb, means in said inner bulb for establishingan arc comprising a pair oi-electrodes, a pair of thermionically activeelements and heating filaments therefor, and a resistance connected inseries between said heating filaments, said electrodes being connectedto said heating filaments whereby the potential drop through saidheating filaments and resistance is impressed across said electrodes,the circuit comprising said heating filaments and resistance beingconnected in series with said incandescent filament between the 3- Alamp comprising a closed outer bulb containing an incandescent filament,a closed inner bulb, means in said inner bulb for establishing an arccomprising a pair of electrodes, a pair of thermionically activeelements and heating filaments therefor, and a resistance connected inseries between said heating filaments, said electrodes being connectedto said heating filaments whereby the potential drop through saidheating filaments and resistance is impressed across said electrodes,the circuit comprising said heating filaments and resistance beingconnected in series heating filaments and resistance is impressed'across said electrodes, and means for connecting said filaments to asource of electrical energy.

5. An electric arc lamp for emitting ultraviolet and visible lightcomprising in combination two bulbs of refractory material adapted totransmit ultra-violet and visible light and positioned one within theother, the outer bulb being provided with a base for insertion into asocket,

said outer bulb containing in addition to the inner bulb a filament ofsubstantial resistance and the inner bulb containing mercury, a pair ofelectrodes each comprising a grid electrically connected to andsurrounding a sleeve coated with material adapted to emit-electrons whenheated, and a heating filament enclosed within each of said sleeves,said filament in vsaid outer bulb and the filaments in the innerbulb-being all connected in series across the terminals of said base andsaid electrodes being connected between the points of greatest potentialdifferences of said filaments within the inner bulb whereby the filamentin the outer bulb serves as a ballast resistance 'for the arc and as asource of visible light. i

6. A lamp comprising two sealed bulbs one within the other, anincandescent filament in .one bulb, the other bulb containing a pair of-metal takes place, and a quantity of thermionically active materialdisposed adjacent eachelectrode and separated from the arc path thereby.

7. A lamp comprising two sealed bulbs one within the other, anincandescent filament in one bulb, the other bulb containing a pair ofspaced unheated electrodes each comprising a coil of without beingheated to a temperature at which evaporation of said metal takes place,and a member having a thermionically active surface disposed adjacenteach electrode and surrounded thereby.

8. A lamp comprising two sealed bulbs one within the other, anincandescent filament in one bulb, the other bulb containing a pair ofspaced unheated electrodes each comprising a coil of refractory metalwire and an'ionizable medium having a suflicient operating pressure tosupport a constricted arc discharge between said electrodes, saidfilament and electrodes being so connected that the lampQzur'rent passesin series through the filament and are path and said elec- 'trodes beingproportioned to carry said current without being heated to a temperatureat which evaporation of said metal takes place, a member comprising asleeve having a thermionically active surface disposed adjacent eachelectrode and screened from the arc path thereby, and a filamentenclosed in each sleeve and insulated therefrom, said enclosed filamentsbeing connected in parallel with the arc path.

9. A lamp comprising two sealed bulbs one within the other, anincandescent filament in one bulb, the other bulb containing a pair ofspaced unheated electrodes each comprising a coil of refractory metalwire and an ionizable medium having a sufficient operating pressure tosupport a constricted arc discharge between said electrodes, saidfilament and electrodes being connected so that the lamp current passesin series through the filament and are path and said electrodes being poportioned to carry said current without being heated to a temperatureat which evaporation of said metal takes place, a

' member comprising a sleeve having a thermionically active surfacedisposed adjacent each electrode and screened from the arc path thereby,and a filament enclosed in each sleeve and insulated therefrom, saidenclosed filaments being connected in parallel with the arc path andeach i V sleeve being electrically connected with its adjacentelectrode.

10. A lamp comprising two sealed bulbs one within the other, anincandescent filament in one bulb, the other bulb containing a pair ofspaced unheated electrodes each comprising a helix of refractory metal,said electrodes and filament being connected so that the lamp currentpasses in series through the filament and arc path and said electrodesbeing proportioned to carry said current without being heated to atemperature at which evaporation of said metal takes place, an ionizablemedium in said are bulb having a suflicient operating pressure tosupport a constricted arc discharge between said electrodes, a

sleeve within eachhelix having a thermionically active surface, and afilament enclosed within each sleeve and insulated therefrom, saidfilamerits being connected-in parallel with the arc path.

within the other, an incandescent filament in one bulb, the'otherbulbcontaining a pair of spaced unheated electrodes each comprising a helixof refractory metal, said electrodes and filament being connected sothat the lamp current passes in series through the filament and are pathand said electrodes being proportioned to carry said current withoutbeing heated to a temperature at which evaporation or said metal takesplace, an ionizable medium in said arc bulb having a suflicientoperating pressure to support a con- 11. A lamp comprising two sealedbulbs one,

' ments being connected in parallel with the arc path and each sleevebeing electrically connected with its adjacent electrode.

12. A lamp comprising two sealed bulbs one within the other, anincandescent filament in one bulb, the-other bulb containing a pair ofspaced unheated electrodes of refractory metal and a quantity ofthermionically active material disposed adjacent each electrode andscreened thereby from the arc path between said electrodes, meansconnecting said electrodes and filament so-that the lamp current passesin series through the filament and are path, and an ioniz able medium insaid bulb comprising a rare gas and a vaporizable material in an amountless than that required to saturate the space in said are bulb at normaloperating temperature of the device but suflicient to supportaficonstricted arc discharge between said electrodes.

13. A lamp comprising two sealed bulbs one within the other, anincandescent filament in one bulb, the other bulb containing a pair ofspaced unheated electrodes of refractory metal and a pair of elementscomprising a thermionically active material, one of said elements beingadjacent each electrode and screened thereby from the arc path "betweensaid electrodes, each element being electrically connected to itsadjacent electrode and said electrodes and filament being connected sothat the lamp current passes in' series through said filament and thearc path between said electrodes, -an ionizable medium in said bulbcomprising a rare gas and a vaporizable material in an amount suflicientto support a constricted arc discharge between said electrodes at normaloperating temperature.

14. A lamp comprising two sealed bulbs one within the other, anincandescent filament in ,one

bulb, the other bulb containing a pair of spaced unheated electrodes ofrefractory metal and a pair of elements comprising a thermionicallyactive material, one of said elements being adjacent each electrode andscreened thereby from the arc path between said electrodes, each-elementbeing electrically connected to its adjacent electrode and saidelectrodes and filament being connected so that the lamp current passesin series through said filament and the arc path between saidelectrodes, an ionizable medium in said bulb comprising a rare gas and avaporizable material in an amount suiiicient to support a constrictedarc discharge between said electrodes at normal opera-ting temperature,said electrodes being proportioned to carry the lamp current withoutbein heated to a temperature at which evaporation of said refractorymetal takes place.

15. An arc lamp comprising a bulb, a pair of spaced unheated arcelectrodes therein each comprising a coil of refractory metal wire, eachcoil surrounding an element comprising a thermionspaced unheated arcelectrodes therein each comprising a coil of refractory metal wire, eachcoil surrounding an element comprising a thermionically active oxide, anionizable medium in said bulb having a suflicient operatingopressure tosupport a constricted arc discharge between said electrodes, saidelectrodesbeing proportioned to carry the arc current without beingheated to a temperature at which substantial evaporation of saidrefractory metal takes place, said bulb being enclosed in an outer bulbto. prevent conduction of heat awayfrom said inner bulb.

17. An arc lamp comprising -a bulb, a pair of spaced unheated arcelectrodes therein comprisingcoils of refractory metal wire, an elementadjacent each electrode comprising a thermionically activeoxide, saidelectrodes being proportioned to carry the arc current without beingheated to a temperature at which substantial evaporation of saidrefractory metal takes place, and a vaporizable material within saidenvelope inan amount which is less than that necessarytto saturate thespace within said bulb at' the normal operating temperature of saiddevice but which and a vaporizable material said envelope in an amountwhich is less .than that necessary to saturate the space within saidbulb at the normal. operating temperature of said device but which issufiicient to support a constricted arc discharge between saidelectrodes, said bulb being enclosed within an outer bulb to preventconduction of heat away from said inner bulb.

19. An arc lamp comprisingabulb, a pair of fl? spaced arc electrodestherein each comprising a helix of refractory metal wire, an elementcoated with a, thermionically active omde within-each helix, saidelement and helix being electrically connected and at the samepotential, and an ionizable medium in said envelope comprising a.vaporizable material in an amount which is less than that necessary tosaturatethe space within said bulb at the normal operating temperatureof said device but which is suflicient to support a constricted arcdischarge between said electrodes.

20. An arc lamp comprising a. bulb, a pair of spaced arc electrodestherein each comprising a helix of refractory metal wire, an elementcoated with a thermionically active oxide within each helix, saidelement and helix being electrically connected and at the samepotential, and an ionizable medium in said envelope comprising avaporizable material in an amount which is less than that necessary tosaturate the space within said bulb at the normal operating temperatureof said. device .but which is suflicient to support a constricted arcdischarge between said electrodes, said bulb being enclosed within anouter bulb to prevent conduction of heataway from said inner bulb. f

21. An arc lamp comprising a. bulb, a pair of spaced unheated electrodestherein of refractory metal, a thermionically active element adjacenteach electrode and with the adjacent electrode interposed between saidelement and the arc path, each of said elements comprising a sleevecoated with refractory oxide and a filament within and insulated fromsaid sleeve, a pair of leads,

.to one of said leads, and an ionizable medium in said envelopecomprising a vaporizable material and having an operating pressuresufilcient to support a constricted arc discharge between saidelectrodes.

22. An arc lamp comprising a bulb, a pair of spaced unheated electrodestherein of refractory metal, a thermionically active element adjacenteach electrode and with the. adjacent electrode interposed between saidelement and the arc path, each of said elements comprising a sleevecoated with refractory oxide and a filament with? in and insulated fromsaid sleeve, each sleeve being electrically connected directly to itsadjacent electrode, a pair of leads, said filaments being connected inseries across said leads and each electrode being connected to one ofsaid leads, and an ionizable medium in said envelope comprising avaporizable material and having an operating pressure sufiicient tosupport a constricted arc discharge between said electrodes.

23. An arc lamp comprising a bulb, a pair of spaced unheated electrodestherein each comprising a helix of refractory metal, a thermion icallyactive element disposed within each helix and comprising a sleeve coatedwith refractory oxide and a filament within and insulated from saidsleeve, a pair of leads, said filaments being connected in series acrosssaid leads and each helix being connected to its adjacent lead, and anionizable medium in said envelope comprising a vaporizable material andhaving an operating pressure suflicient to support a constricted arcdischarge between said electrodes.

24. An arc lamp comprising a bulb, a pair of spaced unheated electrodestherein each comprising a helix of refractory metal, a thermionicallyactive element disposed within each helix and comprising a sleeve coatedwith refractory oxide and a filament within and insulated from saidsleeve,jeach sleeve being electrically connected directly to thesurrounding helix, a pair of leads, said filaments being connected inseries across said leads and each helix being connected to its adjacentlead, and an ionizable medium in said envelope comprising a vaporizablematerial and having an operating pressure sufllcient to support aconstricted arc discharge between said electrodes.

GEORGE SPERI'I.

